1. Field of the Invention
The present invention generally relates to light stable hop fractions. More particularly, it relates to novel methods of preparing such light stable hop fractions and methods of preparing hop flavored beverages using such light stable light fractions.
2. Background of the Art
Hops, in the form of either the ground dried plant or pellets, are used in brewing to give the beverages, such as beer or ale, their characteristic bitter flavor and pleasant aroma. The hops usually are added to the boiling wort in the brewing kettle. Alternatively, if primarily a bitter flavor is desired, a hop extract can be added to the brewing kettle or an isomerized hop extract, if it is highly purified, may be added post kettle, i.e., after the wort has been boiled or after fermentation.
The primary hop constituents which are utilized in the brewing process are the alpha acids, the beta acids, the uncharacterized resins and the hop oils. The alpha acids are known as humulones and the beta acids are known as lupulones. The alpha acids are the precursors of the bitter substances in beer. The beta acids or lupulones have low solubility in wort and beer and they are believed to play a relatively minor role in the brewing process.
During brewing, chemical changes are made in the alpha acids or humulones resulting in the formation of compounds known as iso-alpha acids, i.e., isohumulone, isocohumulone and isoadhumulone. The alpha acids are extracted from the hops by the boiling wort and isomerized to the iso-alpha acids during the kettle boiling stage.
It is known that iso-α-acids derived from hops (or an unreduced hop extract which contains iso-α-acids) can cause light instability in malt beverages. The exposure of such a beverage to light can result in the beverage becoming “light struck” and having a skunky odor. As a result, such beverages cannot be packaged in clear or green glass bottles without a risk of developing the “light struck” character. Light stable beers that can be packaged in clear or green glass bottles are made using reduced hop extracts (i.e., tetrahydroiso-α-acids).
Hop extracts have been used in brewing beer for a number of years. The reasons are several-fold. When whole hops are added to the kettle, the yield of iso-alpha acids is poor, e.g., 10-25% based on the alpha acids present in the hops. However, the conversion of alpha acids in a hop extract to iso-alpha acids can be very high, e.g. 80%. Furthermore, the utilization of the pure iso-alpha acids in a preisomerized extract which is added post kettle is known to be extremely high, e.g. 70-90%.
The production of hop extracts usually consists of extracting the essential bittering acids (e.g., α-acids, β-acids, etc.) from the cellulosic material of the hop blossom by the use of either organic solvents or carbon dioxide. The hop extracts thus obtained can be added to the brewing kettle or chemically processed to isomerize and reduce the alpha acids. The residues from such an extraction are generally referred to as “spent hops” (but are hereinafter referred to as “hop solids”) and they are typically discarded or sold as animal feed.
We have discovered that one disadvantage of adding hop extracts to the wort in the kettle is that the beer produced lacks the full flavor and aroma produced when whole hops are added to the wort in the kettle. As a result, fermented beverages, such as beer, which have been prepared using hop extracts, although they may have the bitterness of beverages prepared from whole hops, do not have the same full hop flavor as fermented beverages made with whole hops. However, the use of whole hops to obtain the full hop flavor results in a very bitter tasting beverages which may not be desired.
There are other disadvantages to using hop extracts. For example, the use of a CO2 or hexane hop extract does not produce a light stable or fully kettle hopped beverage. Also, use of a processed CO2 hop extract (reduced hop extracts) does not produce a fully kettle hopped beverage. It would be advantageous to have a method of preparing less bitter, fermented beverages having the same “full hop flavor” as fermented beverages prepared with the use of whole hops. It would also be advantageous to have a method of making such a beverage which has light stability equal to or better than a beverage made with reduced hop extracts (i.e., tetrahydroiso-α-acids).
U.S. Pat. Nos. 4,767,640; 5,523,489; 5,783,235; 5,874,633; 5,767,319 and U.S. patent application Ser. Nos. 09/111,622; 08/892,898; 08/672,795; 08/659,807; 08/838,217 disclose various hop fractions including hop solids and extracts thereof. These patents and applications are all assigned to the assignee of the present invention. The above-identified patents and applications are hereby incorporated by reference as if fully set forth herein.
Malt beverages made with the hop solids (or extracts thereof) disclosed in the above-referenced patents and applications are generally considered to be light stable.
However, the inventors have found that such malt beverages can still develop off-flavors and aromas when exposed to light. Such light instability is due to the presence of residual α-acids in the hop solids. In the presence of light iso-alpha-acids (isomerized from α-acids during kettle boil) form a compound known as 3methyl-2-butene-1-thiol (hereinafter “3M2B1T”), which is perceived at very low levels as “skunk” off-flavor and aroma. Hence, traditionally hopped beer packaged in a clear or green glass bottle is not light stable.
One traditional method to avoid this light instability was to remove the bittering components or alpha acids from whole hops and chemically alter them in a way so that they cannot form 3M2B1T which then results in light stability of the subsequent product. However, a drawback of hopping a malt beverage with such a chemically altered whole hops is that “kettle hop” flavor and aroma are missing. In this regard, as noted in the above-reference patents and applications, hop solids, a previously discarded byproduct, have great value because they contain the precursors of “kettle hop” flavor and aroma (sometimes referred to as desirable fruity/estery components, which are typically formed during fermentation). However, the inventors have discovered that such hop solids or their extract have enough residual α-acids to affect the light stability of malt beverages.
The inventors have discovered that the sensory threshold for 3M2B1T is as low as one part per trillion (w/w) (1 ppt) in a malt beverage. A method of directly determining 3M2B1T can be found in Goldstein, et al., 51 J. Am. Soc. Brew. Chem. 7-74 (1993). The inventors have now surprisingly discovered that a hexane-washed extract of hop solids will product a malt beverage of unexpectedly superior light stability while lending a kettle hop flavor to the finished malt beverage.
It is important to note that the “full” or “kettle” hop flavor refers to the flavor derived from whole hops or hop pellets after fermentation, not the original aroma of whole hops, hop pellets, CO2 hop extract, or even hop character fraction.